1. Field of the Invention
The present invention relates to a pigment and a method for manufacturing the same. The invention also relates to a yellow toner containing the pigment as a coloring agent and used in recording methods, such as electrophotographic method, electrostatic recording method, magnetic recording method, and toner jet method.
2. Description of the Related Art
Color images are becoming popular and the demand for high-quality images is increasing. In digital full color copy machines and printers, a color image original is subjected to color separation through color filters of blue, green and red, and then a latent image according to the original image is developed with yellow, magenta, cyan and black developers. Accordingly, the coloring agents in the developers are significantly involved in the resulting image quality.
Since yellow coloring agents give the human sense the same impression as other colors, the painting industry requires that yellow coloring agents have high hiding power and high coloring power, and often uses yellow coloring agents having large primary particle sizes. On the other hand, the toner industry requires that coloring agents have high transparency as well as high coloring power, and these are important properties of the coloring agents used in the toner. It has not been considered that coloring agents having large primary particle sizes suitably used in the painting industry can satisfy those requirements at one time.
Japanese Patent Laid-Open No. 11-202558 proposes that C. I. Pigment Yellow 155 be used as a toner coloring agent. According to this patent document, C. I. Pigment Yellow 155 is superior in thermal stability, dispersibility in resins, and chargeability.
Japanese Patent Laid-Open No. 11-242357 proposes that the above issues be solved by appropriately selecting a binding resin to enhance the dispersibility of the coloring agent in the binding resin. For example, by use of a binding resin mainly containing a polyester resin having a specific acid value, even C. I. Pigment Yellow 155, which is difficult to disperse, can be sufficiently dispersed to increase the transparency.
Japanese Patent Laid-Open Nos. 2003-140399 and 2004-212451 propose using C. I. Pigment Yellow 155 in a toner prepared in an aqueous medium. Good transparency can be achieved by maintaining good dispersion of the coloring agent. In addition, this allows easy control of the shape of toner particles, and accordingly, the transfer and cleaning properties of the toner can be improved.
The above-cited documents, however, do not discuss that when C. I. Pigment Yellow 155 having a small primary particle size is dispersed in a medium such as an organic solvent, the viscosity of the dispersion is increased.